[OBSD Programming] how to wait for input?

[Christian Schäfer <caefer_(_at_)_krachstoff_(_dot_)_net>]

hi all!

I think I have a problem that must have been adressed several times 
before regarding unix programming. but except hints of a possible 
solution, all I can find is a bunch of man pages that I can not yet use 
altogether to achieve what I need. maybe with your help I can understand 
 the way I have to go..


the goal of what I and some others are programming is two communication 
pipes to a external device (here a cisco switch or router).

we can access the device by

	$ cu -s 9600 -l /dev/tty00

since we do not want to re-invent the wheel, we want to use cu/tip to do 
the communication work for us. so we execvp() the command, fork() it and 
dup2() stdin and stdout to our pipes. so we have a reading and a writing 
pipe to that process. this works already.

that the device is in canonical mode and we read  all characters from 
that device until a linefeed (\n) occurs. we then can process this input 
as a string.

but this device often send a prompt, that is a string _not_ ending with 
a linefeed. we can only know a promt when there is something read from 
the pipe followed by a period of nothing.

we want to read this as well and add the linefeed manually.

now what I do not know is, how can I read from a pipe (FILE*) and 
timeout at some point?

getc() will try to read forever when there is nothing send. we need a 
safe way to know if there actaully _is_ something to read first.

something like this:

while(..)
{
	switch(is_there_something(pipestream, TIMEOUT_IN_MSEC))
	{
		case -1: /* some error occured */ break;
		case 0;  /* nothing to read therefor timed out */
		default; /* read something */
	}
}


can this be done? I hope so.
need some urgend reply here.

if I can pass some more information, please ask.


thanks in advance!


regards
/christian